1. Field of the Invention
The present invention relates to an optical disc playback apparatus, and particularly, to control of a pickup unit for reading data from an optical disc.
2. Description of the Background Art
As media for recording data, DVDs (Digital Versatile Discs), BDs (Blu-Ray Discs), and other optical discs are known. The data recorded on an optical disc is read by a pickup apparatus that emits laser light. In order to read data recorded on the optical disc, it is necessary to condense the laser light so that the light is applied as focused on a data recording surface of the optical disc. To this end, an objective lens constituting the pickup apparatus is moved in the focusing direction of the optical disc.
On the other hand, what is called a working distance in playing back a BD (about 0.5 mm), for example, is shorter than a working distance in playing back a DVD (about 1.5 mm), and therefore the lens and the optical disc may collide. A working distance herein refers to the distance between the objective lens and the surface of the optical disc when the focus is attained at the data recording layer of the optical disc.
For example, Japanese Patent Laying-Open No. 2004-192784 discloses a technique of realizing precise focus jump while avoiding collision of an optical disc and a focusing lens.
Japanese Patent Laying-Open No. 2006-134367 discloses a technique of avoiding contact between an objective lens and a disc surface in discriminating an optical disc.
Japanese Patent Laying-Open Nos. 2004-192784 and 2006-134367 both disclose that what is called an S-shape curve is employed in controlling movement of the lens. However, if the S-shape curve is not detected, the movement of the lens is not controlled and thus the lens may possibly collide with the optical disc.